Emulsion ink

ABSTRACT

PCT No. PCT/GB97/00070 Sec. 371 Date Oct. 27, 1998 Sec. 102(e) Date Oct. 27, 1998 PCT Filed Jan. 10, 1997 PCT Pub. No. WO97/25383 PCT Pub. Date Jul. 17, 1997Ink comprising a water-in-oil emulsion consisting of an aqueous phase and an oil phase and a coloring agent, wherein the oil phase comprises at least about 25% w/w of a silicone oil and an emulsifier.

FIELD OF THE INVENTION

The present invention relates to an emulsion ink whose consumption levelis substantially constant with temperature. The ink is particularlyuseful on digital and stencil duplicators, but may also be useful inother printing applications, e.g. letterpress and silk-screen printing.

BACKGROUND OF THE INVENTION

Inks for use on digital duplicators and stencil duplicators aregenerally based on water-in-oil emulsions, although the use ofnon-emulsion inks is also known. Examples of conventional water-in-oilemulsion inks are disclosed in U.S. Pat. No. 5,378,739.

JP-A-6,128,516 discloses a water-in-oil emulsion ink for use in astencil printing method and which has improved set-off properties. Theink includes a thermosetting or a hot-melting component in the oil phaseand a siliccone oil in the aqueous and/or oil phase in an amount of 1 to20% w/w based on the total ink. In the inks exemplified the amount ofsilicone oil in the oil phase is at most 21.6% w/w.

A disadvantage with such inks is that their consumption level isdependent upon temperature, and consequently they give varying printquality depending on the temperature of the operating environment.Aspects of print quality which relate to ink consumption, and thereforeink temperature, include print density, set-off and solid area infill.

EP-A-0,661,356 discloses a water-in-oil emulsion ink said to haveimproved temperature dependence. The ink contains a water-insolublecolouring agent in the aqueous phase thereby avoiding the need for aresinous dispersing agent in the oil phase. While a degree oftemperature independence is achieved, this is only significant at thelower end of the normal operating range, and not over the whole range.

SUMMARY OF THE INVENTION

According to the present invention, an ink comprises a water-in-oilemulsion consisting of an aqueous phase and an oil phase, and acolouring agent, wherein the oil phase is a continuous phase andcomprises at least 25% w/w of a silicone oil, and an emulsifier.

Provided that the silicone oil is present in sufficient concentration,the ink consumption in a digital or stencil duplicator, at least, islargely independent of temperature over the normal operating range, eg.around 10-35° C.

DESCRIPTION OF THE INVENTION

The silicone oil used in the present invention is incapable of formingan emulsion in the absence of a suitable emulsifier. Any suitableemulsifier may be used, but preferably the emulsifier is asilicone-based emulsifier as better miscibility with the silicone oiland better emulsion stability can be achieved with an emulsifier of thistype.

In its simplest form, the oil phase comprises only emulsifier andsilicone oil. In this case, the Emulsifier is preferably soluble in thesilicone oil, but this is not essential as simple water-in-siliconeemulsions can be achieved with emulsifiers that are insoluble in thesilicone oil; see for instance "A Guide to Formulating Water-in SiliconeEmulsions with Dow Corning 3225C Formulation Aid", Dow Corning 1995.Examples of emulsifiers that are soluble in silicone oils are disclosedin U.S. Pat. No. 5,132,047, and comprise alkyl siloxane polymersmodified by a polyether group, or other substituent, attached to one ofthe terminal silicon atoms thereof.

It may be desirable to include a third component in the oil phase, toalter the properties of the ink according to the printing application,or to increase the miscibility of the emulsifier with the silicone oil.In this case, it is essential that the silicone oil at least is solublein the third component, so as to form a substantially continuous oilphase. Preferably, the emulsifier is also soluble in the thirdcomponent.

Examples of emulsifiers that are immiscible with the silicone oil,either totally, or as a result of the proportions of these components inthe oil phase, and with which it may be desirable to use a thirdcomponent as described above, include alkyl siloxane polymers havingpolyether side chains, of the general formula: ##STR1## in which R is aC₁₀ or above alkyl group, for instance lauryl or cetyl, and R' ispolyether. X and Y can vary widely, but examples of suitable ranges areX=1-100 and Y=1-40.

Examples of components used to increase the miscibility between thesilicone oil and the emulsifier include hydrocarbon oils or solvents andcyclomethicones having the general formula: ##STR2## in which n=3, 4 or5.

The cyclomethicones all tend to be volatile, whereas hydrocarbon oils orsolvents used may be volatile or involatile. The use of a volatile thirdcomponent may be preferred if its volatility is comparable to that ofwater thereby allowing the water/oil balance of the emulsion to bemaintained despite evaporation during use on the printing machine.However, a disadvantage associated with the use of some volatilecomponents is that their loss to the atmosphere may be sufficient tocause separation of the oil phase, resulting in collapse of the emulsionstructure.

It is thought that the benefits which result from incorporating asilicone oil decrease as the proportion of the third component in theoil phase increases, assuming a constant proportion of emulsifier.Therefore, it is desirable to minimise the proportion of the: thirdcomponent, preferably adding just sufficient to achieve solubility ofthe emulsifier.

The amount of emulsifier used in the ink composition need only besufficient to achieve a stable water-in-oil emulsion. Typically, it ispresent in an amount of at least 1% or 2% w/w based on the total inkcomposition, although lower amounts may be used provided that thestability of the emulsion is not adversely affected. Very highemulsifier concentrations should preferably be avoided, as these willinevitably reduce the amount of silicone oil present in the inkcomposition. At least one co-emulsifier may also be included in the inkcomposition, to promote formation of the water-in-oil emulsion. Onesuitable example is triglyceryl-4-isostearate.

The oil phase concentration in the ink of the present invention can varyin the range 10 to 80% w/w, although concentrations outside this rangemay also be useful depending upon the emulsifier used. Typically,however, the oil phase concentration is in the range 15 to 50% w/w,preferably 20 to 30% w/w, and more preferably 20 to 25% w/w.

As mentioned above, when the oil phase comprises both silicone oil andhydrocarbon oil/cyclomethicone preferably the amount of silicone oil ismaximised. The amount of silicone oil should be at least about 25% w/wof the oil phase, and is preferably at least about 30% w/w, and morepreferably at least about 40% w/w, and most preferably at least about50% w/w. However, it is apparent that there is latitude to vary theproportions of these two components outside these ranges and stillachieve ink consumption which is substantially constant over a typicaloperating range of 10 to 35° C. By substantially constant we mean thatthe variation in ink consumption between the extremes of thistemperature range (i.e. 10° C. and 35° C.) and ambient temperature(approx. 21° C.) is typically less than about 20%, preferably less than15%, and more preferably less than 10%, as tested on a digitalduplicator of the type described in the Example below. However,variations in consumption higher than these may be acceptable, dependingon the printing application in which the ink is to be used.

Suitable silicone oils for use in the ink of the present inventioninclude poly(dialkylsiloxane) oils, preferably poly(dimethylsiloxane)oils, such as those commercially available e.g. from Dow Corning, atvarying molecular weights, and poly(arylalkylsiloxane) oils, such aspoly(phenylmethylsiloxane) oils. The most preferred silicone oils arethe poly(dimethylsiloxane) oils.

The coloration of the ink of the present invention is provided by acolouring agent which may be a pigment or a dye. The colouring agent maybe located in the oil phase or in the aqueous phase of the ink, asdesired, by means of conventional techniques, such as selection of anappropriate dispersant. Carbon black is normally used as the colouringagent for black ink and conventional organic pigments are used for othercoloured inks, e.g. phthalocyanine blue. The amount of colouring agentused depends upon its type and in which phase it is to be dispersed; itcan be up to 30% w/w based on the total ink composition, but is oftenless than this, for instance up to 10% w/w, e.g. 3-7% w/w carbon.

It may be necessary to vary the composition of the ink of the presentinvention, for instance with respect to the amount and viscosity of theoil phase and thet water content, according to the printing application,and in some cases according to the particular duplicator or otherapparatus being used.

The ink composition of the present invention may contain additional,conventional ink components, for example, resins (water and/or oilsoluble), stabilisers, extenders, waxes, anti-freeze agents, pigmentdispetrsants, biocides and other components known to modify emulsioninks to beneficial effect.

The present invention is now illustrated by the following Example andthe accompanying Figure.

EXAMPLE 1

Three inks were made to the formulations shown in Table 1 using themethod outlined below.

                  TABLE 1                                                         ______________________________________                                                         INK 1  INK 2   INK 3                                         ______________________________________                                        OIL PHASE COMPONENTS %                                                        Poly(dimethylsiloxane):                                                                          13.6     6.8     0                                         DC 200 5 cSt (5 × 10.sup.-6 m.sup.2 /s)                                 (Dow Corning)                                                                 Hydrocarbon Distillate:                                                                          4.6      11.4    9.5                                       Paraset 26H                                                                   (Carless Refining and                                                         Marketing)                                                                    Hydrocarbon Oil:   0        0       8.7                                       Texnap 46                                                                     (Texaco)                                                                      Emulsifier:        2.0      2.0     2.0                                       Tegopren 7008                                                                 (Th Goldschmidt)                                                              Co-Emulsifier:     2.8      2.8     2.8                                       Isolan G1 34                                                                  (Th Goldschmidt)                                                              Diluent for Emulsifier                                                                           2.0      2.0     2.0                                       Blends:                                                                       Hexyl Laurate for Ink 1                                                       Process Oil G217 (Texaco)                                                     for Inks 2 & 3                                                                AQUEOUS PHASE COMPONENTS %                                                    Water              51.2     50.4    50.4                                      Pigment:           15.3     16.1    16.1                                      28% Carbon Dispersion in                                                      Water (27% C for Inks 2 & 3)                                                  Stabiliser:        1.0      1.0     1.0                                       Lithium Chloride for Ink 1                                                    Potassium Sulphate for Inks                                                   1 & 3                                                                         Anti-freeze Agent: 7.5      7.5     7.5                                       Ethylene Glycol                                                               TOTAL              100      100     100                                                          INK 1    INK 2   INK 3                                     % Siloxane in Oil Phase                                                                          54.4     27.2    0                                         % Siloxane in ink  13.6     6.8     0                                         ______________________________________                                    

Method

Preparation of Oil Phase

An emulsifier blend was made by mixing Tegopren 7008 (1 part) Isolan GI34 (1.4 parts) and hexyl laurate (1 part), until a clear homogeneousliquid was obtained.

The oil phase was then prepared by adding in succession to a 1 litrevessel: emulsifier blend (27.3 g), Paraset 26H (18.2 g) and 5 cSt DC 200Fluid (54.5 g). These were mixed using a stirrer fitted with a paddleblade at moderate speed for 2 minutes.

Preparation of Aqueous Phase

The components were added to a second vessel in succession: lithiumchloride (3.7 g), aqueous carbon dispersion (61.3 g), ethylene glycol(30 g) and water (204.9 g) and stirred for 5 minutes.

Preparation of Emulsion Ink

The oil phase was stirred at moderate speed and a 2.0 ml portion of theaqueous phase was added dropwise with stirring, and stirring continuedfor a period of 1 minute. Thereafter, stirring was continued and theremainder of the aqueous phase was added over a period of 17 minutes.The resultant emulsion was then stirred with a 3-blade propeller stirrerfor 2 minutes at moderate speed and for a further 3 minutes at highspeed, at which point significant thickening occurred.

Table 2 shows the consumption and print densities of Ink 1 in comparisonwith a standard Gestetner ink grade CPT1 as tested on a GestetnerCopyPrinter (registered trademark) digital duplicator.

FIG. 1 is a graph of ink consumption results of Ink 1 and standard inkCPT1, on the basis of both inks giving a nominal consumption of 1 at 21°C.

Ink 1 shows considerably less variation in consumption than the standardCPT1 ink.

Table 3 shows the relative consumptions of Ink 2, which is an inkaccording to the invention, and Ink 3, which contains no silicone oil,as tested on a Gestetner CopyPrinter digital duplicator 5380.

Ink 3 is of lower viscosity than ink CPT1, and consequently shows lessvariation in consumption than CPT1. Irrespective of this, Ink 2 showsconsiderably less variation in consumption than Ink 3.

                  TABLE 2                                                         ______________________________________                                        Digital                                                                       Duplicator                                                                    Model                                                                         Temper-      5380          5375                                               ature/° C.                                                                          10       21       21     33                                      ______________________________________                                        Ink     Ink 1    18.4     20.0   29.8   30.3                                  Consump-                                                                              Gestetner                                                                              9.4      13.3   16.3   21.6                                  tion.sup.1 /g                                                                         CPT1                                                                  Print   Ink 1    1.02-1.08                                                                              1.01-1.04                                                                            1.14-1.17                                                                            1.15-1.18                             Density.sup.2                                                                         Gestetner                                                                              0.79-0.81                                                                              0.87-0.94                                                                            0.92-0.98                                                                            1.03-1.08                                     CPT1                                                                  ______________________________________                                         .sup.1 Ink consumption is the weight of ink (g) to print 250 test prints      on a specified standard paper using a standard Gestetner test original        (approximately 15% coverage) made at default print speed.                     .sup.2 Print density was measured using a MacBeth RD914 reflection            densitometer.                                                            

                  TABLE 3                                                         ______________________________________                                                       INK 2         INK 3                                                           (Invention)   (Reference)                                      Temp (° C.)                                                                             20     30       20   30                                      ______________________________________                                        Consumption (g)  27.8   32.9     23.2 29.2                                    Consumption Relative To                                                                        1      1.2      1    1.3                                     Unity At 20° C.                                                        % Change in Consumption                                                                        --     +18.3    --   +25.9                                   From 20° C.                                                            ______________________________________                                    

What is claimed is:
 1. Ink comprising a water-in-oil emulsion consistingof an aqueous phase and an oil phase, and a colouring agent, wherein theoil phase is a continuous phase and comprises at least about 25% w/w ofa silicone oil, and an emulsifier.
 2. Ink according to claim 1, whereinthe oil phase comprises at least about 30% w/w silicone oil.
 3. Inkaccording to claim 2, wherein the oil phase comprises at least about 40%w/w silicone oil.
 4. Ink according to claim 3, wherein the oil phasecomprises at least about 50% w/w silicone oil.
 5. Ink according to anypreceding claim, wherein the emulsifier is a silicone-based emulsifier.6. Ink according to any preceding claim, wherein the oil phase furthercomprises a component in which the silicone oil is soluble.
 7. Inkaccording to claim 6, wherein the said component is a hydrocarbon oil orsolvent.
 8. Ink according to claim 6, wherein the said component is acyclomethicone having the formula: ##STR3## in which n=3, 4 or
 5. 9. Inkaccording to any preceding claim, wherein the silicone oil is apoly(dialkylsiloxane) oil or a poly(arylalkylsiloxane) oil.
 10. Inkaccording to claim 9, wherein the silicone oil is apoly(dimethylsiloxane) oil.
 11. Ink according to any preceding claim,wherein the oil phase comprises 10 to 80% w/w of the total ink.
 12. Inkaccording to claim 11, wherein the oil phase comprises 15 to 50% w/w ofthe total ink.
 13. Ink according to claim 12, wherein the oil phasecomprises 20 to 30% w/w of the total ink.
 14. Ink according to anypreceding claim, wherein the colouring agent is in the oil phase. 15.Ink according to any of claims 1 to 14, wherein the colouring agent isin the aqueous phase.
 16. A method of printing an article by applying,through the use of a printing apparatus, to said article an inkcomprising a water-in-oil emulsion consisting of an aqueous phase and anoil phase, and a coloring agent, wherein the oil phase is a continuousphase and comprises at least about 25% w/w of a silicone oil, and anemulsifier.
 17. A method according to claim 16, wherein the ink isapplied to said article using, as said printing apparatus, a stencilduplicator.
 18. A method according to claim 16, wherein the ink isapplied to said article using, as said printing apparatus, a digitalduplicator.